Isolated human tau peptide epitope which specifically binds monoclonal antibody AT120.

ABSTRACT

An isolated human tau peptide epitope which specifically binds monoclonal antibody AT120 consisting of the amino acid sequence selected from the group consisting of SEQ ID Nos. 2, 3, 4, 15, 16, 17, 18, 19 and 20.

PRIOR APPLICATION

This application is a division of U.S. patent application Ser. No. 08/403,917 filed Jan. 19, 1995, now U.S. Pat. No. 6,010,913 which is a continuation-in-part of U.S. patent application Ser. No. 08/403,916, filed Jan. 19, 1995 now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 08/244,951 filed Jan. 19, 1995 now U.S. Pat. No. 5,843,779 which is a continuation-in-part of PCT application Ser. No. EP93/03499 filed Dec. 10, 1993.

The invention relates to new monoclonal antibodies directed against the human microtubule-associated protein tau, to the hybridomas secreting these monoclonal antibodies, and to the antigen recognition by these monoclonal antibodies and their applications. The invention also relates to a process for diagnosing brain diseases involving the particular epitope (of the tau protein) which is recognized by said monoclonal antibodies.

Alzheimer's disease (AD) is the most common form of adult-onset dementia. At present, no biochemical test is available for antemortem diagnosis of AD. The disease is therefore clinically diagnosed primarily by exclusion of other forms of dementia. The illness is characterized neuropathologically by the presence of neuritic (senile) plaques and neurofibrillary tangles (NFT).

Neurofibrillary tangles consist of paired helical filaments (PHF), of which the main protein component is a modified form of the microtubule-associated protein tau (Brion et al., 1985; Greenberg and Davies, 1990; Lee et al.,1991), which under normal circumstances promotes microtubule assembly and stability (Weingarten et al., 1975; Bré and Karsenti, 1990), which is synthesized in the neurons of several species, including humans (Kosik et al., 1989) and which is abundantly present in the axonal compartment of these neurons (Binder et al., 1985).

The protein exists as a family of different isoforms of which 4 to 6 isoforms are found in normal adult brain but only 1 isoform is detected in fetal brain (Goedert et al., 1989). The diversity of the isoforms is generated from a single gene by alternative mRNA splicing (Himmler, 1989). The most striking feature of tau protein, as predicted from molecular cloning, is a stretch of 31 or 32 amino acids occurring in the carboxy-terminal part of the molecule that is repeated 3 or 4 times. Additional diversity is generated through 29 or 58 amino acid-long insertions in the NH₂-terminal part of the molecules (Goedert et al., 1989).

Tau variants of 64 and 69 kDa, which are abnormally phosphorylated, as revealed by the apparent increase in their molecular mass observed after alkaline phosphatase treatment, have been detected exclusively in brain areas showing neurofibrillary tangles and senile plaques (Flament et al., 1989, 1990). The sites of phosphorylation by 4 different kinases have been mapped in the C-terminal microtubule-binding half of tau, and it could be shown that the action of a calcium calmodulin-dependent kinase on bacterially expressed tau resulted in the phosphorylation of Ser(405) which induced a lower electrophoretical mobility (Steiner et al., 1990). Tau present in paired helical filaments, called PHT-tau is abnormally phosphorylated (Lee et al., 1991). This abnormal phosphorylation causes a conformational change in tau, resulting probably in self-association and the formation of PHFs. PHF-tau in AD is phosphorylated at several sites, one of which is the phosphoserine 199 and/or 202. This site is specifically recognized by a mAb called AT8 (Biernat et al., 1992). Therefore, AT8 is a discriminative marker for PHF-tau (Goedert et al., 1992).

Several antibodies have been reported that show reactivity to human tau either because they are directed to non-specific phosphorylated epitopes present on neurofilament and subsequently shown to cross-react with normal and abnormally phosphorylated tau (Nukina et al., 1987; Ksiezak-Reding et al., 1987) or because they recognized specific epitopes on normal and abnormally phosphorylated tau (Kosik et al., 1988). In addition to the tau antibodies directed towards non-specific epitopes, antibodies directed specifically to phosphorylated tau epitopes have been described (Mercken et al., 1992b).

Although overall tau mRNA levels are only slightly modulated in Alzheimer-affected brain regions (Goedert et al., 1988; Barton et al., 1990) it has been shown that total tau protein levels may differ at least 6-fold (Khatoon et al., 1992). This has been demonstrated by polyclonal antibodies against tau (Flament and Delacourte, 1990) and by monoclonal antibodies directed to well-defined epitopes. The Alz 50 monoclonal antibody recognizing a phosphate-independent epitope in the N-terminus of the tau molecule (Goedert et al., 1991) has been used in a sandwich immunoassay on brain homogenates and it has been shown that tau levels are higher in Alzheimer's patient brains (Ghanbari et al., 1990; patent application EP 444 856).

An antibody named “423”, raised against pronase-treated PHFs and specifically reactive with a 9.5 kDa and a 12 kDa fragment was also used to measure tau protein in Alzheimer's disease (patent application WO 89/03993). Similarly, it was found that increased mAb 423 immunoreactivity was observed in Alzheimer brain homogenates as compared with control brain homogenates.

Mercken et al. (1992b) describe a range of monoclonal antibodies which are either specific for a phosphatase-sensitive epitope (AT8) or which react with PHF-tau as well as with normal tau (AT1, AT4, AT6, AT9, ATI 1, AT12 and AT14) in Western blotting.

Moreover, the antibody tau 1 (Wischik et al., 1988; Harrington et al., 1990) was also used to measure tau in brain homogenates. In one case when tau levels were specifically measured in Alzheimer-affected brain sections, tau levels were eight-fold higher as compared with levels in normal brain homogenates (Khatoon et al., 1992).

In a first attempt to diagnose Alzheimer disease in cerebrospinal fluid, the PHF-tau-specific monoclonal antibody AT8 (Mercken et al., 1992b), was used. However, no PHF tau antigen could be demonstrated.

Thus far, none of the monoclonals that have been described have been successful in detecting tau in non-concentrated cerebrospinal fluid (CSF), although the presence of tau was observed in 100-fold concentrated CSF (Wolozin and Davies, 1987) or in CSF samples using polyclonal antibodies (Delacourte and Vermersch, 1991).

The aim of the present invention is therefore to provide monoclonal antibodies which allow reliable and sensitive detection of normal and abnormally phosphorylated tau present in brain extracts and in unconcentrated cerebrospinal fluid. The invention also aims at providing the hybridoma which secretes the above-said monoclonal antibodies.

The invention furthermore aims at providing the epitope of the tau protein present in brain homogenates or in body fluids such as cerebrospinal fluid, which is recognized by said monoclonal antibodies.

The invention aims at providing a process for the detection or diagnosis in vitro of brain diseases involving tau protein.

The monoclonal antibodies of the invention are characterized by the fact that they react with an epitope which is present in both normal and abnormally phosphorylated human tau protein. The monoclonal antibodies are furthermore characterized by the fact that they form an immunological complex with an epitope or an antigen belonging to normal and abnormally phosphorylated human tau protein. The monoclonal antibodies of the invention are also characterized by the fact that they do not form an immunological complex with other phosphorylated proteins such as MAP-1, MAP-2 and neurofilaments which share part of their sequence with tau protein (Nukina et al., 1987; Lewis et al., 1988) as determined by means of an ELISA. The monoclonal antibodies of the invention are also characterized by the fact that they are liable to detect human tau protein in CSF, with said tau protein being at a concentration as low as 1.0 pg/ml and with said tau protein being detected at 100% recovery upon the addition of a fixed amount of tau protein in tau protein-negative CSF (100% spiking recovery).

The monoclonal antibodies of the invention also enable the diagnosis of Alzheimer's disease (AD) on the basis of CSF, i.e., to detect tau and modified forms of tau in CSF. The problem associated herewith is that this antigen is present in a very low amount in CSF, therefore the detection assay must be very sensitive. This problem can be resolved by using the combination of the monoclonal antibody of the invention together with the catalysed reporter deposition amplification technique (CARD, Bobrow et al., 1989), allowing a tau-specific CARD ELISA with a higher sensitivity. Alternatively, a mixture or combinations of labeled monoclonal antibodies, each recognizing epitopes different from AT120 epitope, could be used as detector antibodies.

The results obtained with the monoclonal antibody secreted by the hybridoma AT120 of the invention indicate that elevated tau levels are not only found in AD, but also in other neurological diseases where neuronal death or damage occurs.

The expression “form an immunologically complex with” means that the monoclonal antibody of the invention binds to the above-said antigen under one of the following conditions as mentioned in the techniques below:

Light Immunomicroscopy

Brain tissue samples, obtained at surgery or autopsy, are fixed by immersion in 4% formalin or Bouin's fixative and embedded in paraffin for sectioning. The monoclonal antibodies of the invention are applied in conjunction with a technique to visualize the formed immune complexes such as the avidin-biotinylated peroxidase complex technique (Hsu et al., 1981) using 3,3′-diaminobenzidine tetrahydrochloride for development of color. Sections are counterstained with Harris haematoxylin stain.

Immunoelectron Microscopy in Tissue Sections

Brain tissue samples, obtained at surgery or autopsy are fixed in either Bouin's fixative or 10% buffered formalin before sectioning without embedding (Vibratome). The monoclonal antibody of the invention is used for immunostaining by the indirect immunogold method after which the sections are fixed, embedded and sectioned for electron microscopy, all according to standard protocols known to those skilled in the art (Brion et al., 1985).

Immunoblotting Procedures

For immunoblotting, fractions enriched in tau are prepared as described (Lindwall and Cole, 1984). Typically, 50 g of brain tissue is cut into small pieces with scissors and homogenized 1:1 (wt/vol) in buffer A (20 mM 2-[N-morpholino]ethanesulfonic acid, 80 mM NaCl, 2 mM EDTA, 0.1 mM EGTA, 1 mM β-mercaptoethanol, pH 6.75) with a Potter homogenizer equipped with a Teflon plunger. The homogenate is centrifuged for 1 h at 150,000 g at 4° C., and the supernatant is heated for 5 min in boiling water and chilled again for 10 min on ice. The slurry is centrifuged for 2 h at 150,000 g at 4° C., and the supernatant is collected. The heat-stable cytosolic extract is added to 2.5% perchloric acid and centrifuged for 1 h at 150,000 g at 4° C., after which the supernatant is neutralized with 3 M Tris. The supernatant is then dialyzed in water and concentrated in a Centriprep concentrator (Amicon, Lausanne, Switzerland).

SDS-polyacrylamide electrophoresis is performed under reducing conditions on 12% gels (Laemmli, 1970). After electrophoresis, the proteins are either fixed and stained with Coomassie brilliant blue, or transferred (Towbin et al., 1979) to nitrocellulose sheets (Hybond-C, Amersham) or Immobilon filters (Millipore).

After transfer, the filters are presoaked in PBS containing 0.05% (v/v) Tween 20 (Tween-PBS) and then incubated for 1 h in Tween-PBS containing 5% (w/v) skimmed dried milk and 10% (v/v) newborn calf serum (blocking buffer). Next, the filters are treated overnight at 4° C. with a monoclonal antibody according to the invention appropriately diluted in blocking buffer.

The filters are then washed three times in Tween-PBS and treated for 1.5 h at room temperature with horseradish peroxidase-labeled rabbit anti-mouse IgG (Dakopatts, Denmark) diluted {fraction (1/3000)} in blocking buffer. After three washes in Tween-PBS, streptavidine-biotinylated horseradish peroxidase complex (Amersham), diluted {fraction (1/250)} in blocking buffer, is applied for 1.5 h at room temperature. Thereafter, the filters are washed three times in Tween-PBS and once in PBS. The filters are then incubated in PBS containing 0.05% (w/v) diaminobenzidine and 0.03% (v/v) hydrogen peroxide until background staining develops.

It should be clear that the formation of an immunological complex between the monoclonal antibodies and the antigen is not limited to the precise conditions described above, but that all techniques that respect the immunochemical properties of the antibody and antigen binding will produce similar formation of an immunological complex.

Human normal tau is a class of at least six tau proteins ranging in molecular weight from 58 to 64 kDa which are specifically expressed in the somatodendritic domain of all neurons (Papasozomenos and Binder, 1987). Moreover Alzheimer (tangle)-specific tau forms have been described which occur in the degenerating cortical neurons of Alzheimer's disease or Down's Syndrome and of which the lower electrophoretic mobility can be attributed to abnormal phosphorylation (Flament et al., 1989; Delacourte et al., 1990).

According to an advantageous embodiment of the invention, the monoclonal antibody forms an immunological complex with all forms of tau described above, with said human tau protein being liable to be obtained from a brain homogenate, itself isolated from the cerebral cortex of a patient suffering from a neurological disease.

A “brain homogenate” and tau protein can be obtained by the man skilled in the art according to standard methods such as the method of Lindwall and Cole (1984).

According to an advantageous embodiment, the monoclonal antibodies of the invention form an immunological complex:

either with an epitope located within the following amino acid sequence of human tau protein:

      155                 160                 165 (SEQ ID NO 1) NH₂- Arg Gly Ala Ala Pro Pro Gly Gln Lys Gly Gln Ala Asn Ala     170                 175                 180 Thr Arg Ile Pro Ala Lys Thr Pro Pro Ser Ser Glu Glu Pro Pro     185                 190                 195 Lys Ser Gly Glu Pro Pro Lys Ser Gly Asp Arg Ser Gly Tyr Ser     200                 205                 210 Ser Pro Gly Ser Pro Gly Thr Pro Gly Ser Arg Ser Arg Thr Pro     215                 220 Ser Leu Pro Thr Pro Pro Thr Arg

more specifically with an epitope located within the following amino acid sequence:

199 200                 205                 210 (SEQ ID NO 2) Ser Pro Gly Ser Pro Gly Thr Pro Gly Ser Arg Ser Arg Thr Pro     215                 220                 225 Ser Leu Pro Thr Pro Pro Thr Arg Glu Pro Lys Lys Val Ala Val     230 231 Val Arg Thr

more specifically with an epitope located within the following amino acid sequence:

207         210                 215 (SEQ ID NO 3) Gly Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr Pro Pro

most specifically with an epitope located within the following amino acid sequence:

218                     224 (SEQ ID NO 4) Pro Pro Thr Arg Glu Pro Lys

or with any other peptide capable of forming an immunological complex with a monoclonal antibody, which is capable of forming a complex with an epitope located in a tau protein regions as shown in any of SEQ ID NO 1 to 4.

The sequences as shown in SEQ ID NO 1 to 4 will be hereafter designated as containing “the epitope” of the invention. Amino acid sequence 1 spans the amino acids 155-221 of human tau using the numbering of human tau 40, amino acid sequence 2 spans the amino acids 199-231 of human tau, amino acid sequence 3 spans the amino acids 207-219 of human tau, and amino acid sequence 4 spans the amino acids 218-224 of human tau (Goedert et al., 1989).

The peptides capable of forming an immunological complex with a monoclonal antibody, which itself is liable to form a complex with the above-mentioned peptide will be defined as the “variant peptides”.

A preferred monoclonal antibody of the invention is secreted by the hybridoma deposited at ECACC (European Collection of Animal Cell Cultures, Vaccine Research and Production Laboratory, Public Health and Laboratory Service (PHLS), Centre for Applied Microbiology and Research, Proton Down, GB-Salisbury, Wiltshire SP4 OJG) on Oct. 8, 1992 under No. 92100853.

This hybridoma will be hereafter designated as “hybridoma AT120” and the secreted monoclonal antibody will be designated as “monoclonal antibody AT120”.

The invention also relates to the hybridoma which secretes a monoclonal antibody according to the invention, and particularly the hybridoma filed at ECACC on Oct. 8, 1992 under No. 92100853.

The above-mentioned monoclonal antibodies are obtained by a process involving obtention and isolation of hybridomas which secrete these monoclonal antibodies.

A process for obtaining the hybridoma involves:

starting from spleen cells of an animal, e.g. mouse or rat, previously immunized in vivo, or from spleen cells of such cells previously immunized in vitro with an antigen recognized by the monoclonal antibody deposited at ECACC on Oct. 8, 1992 under No. 92100853, or with a peptide containing or which are constituted by parts of any of the sequences as represented in SEQ ID NO 1 to 4;

fusing said immunized cells with myeloma cells under hybridoma-forming conditions; and

selecting those hybridomas which secrete the monoclonal antibodies which specifically recognize an epitope of the above-said antigen and which form an immunological complex with normal tau or the abnormally phosphorylated form of tau protein or with the peptide comprising the epitope of tau recognized by the monoclonal antibody of the invention.

A process for producing the corresponding monoclonal antibodies involves:

culturing the selected hybridoma as indicated above in an appropriate culture medium; and

recovering the monoclonal antibodies secreted by said selected hybridoma; or alternatively

implanting the selected hybridoma into the peritoneum of a mouse and, when ascites has been produced in the animal;

recovering the monoclonal antibodies then formed from said ascites.

The monoclonal antibodies of the invention can be prepared by conventional in vitro techniques such as the culturing of immobilized cells using e.g. hollow fibers or microcapsules or such as the culturing of cells in homogeneous suspension using e.g. airlift reactors or stirred bioreactors.

The invention also relates to a peptide (antigen), which can be obtained from a human brain homogenate itself being isolated from the human cerebral cortex obtained from a patient having Alzheimer's disease, and which forms an immunological complex with the monoclonal antibody of the invention.

The invention also relates to peptides (antigens) which are liable to form an immunological complex with anyone of the monoclonal antibodies of the invention and

which are contained in or are constituted by parts of the sequence as shown in SEQ ID NO 1, 2, 3, or 4;

which contain or are constituted by the sequence of the variant peptides defined above.

It is to be recalled that variant peptides are those peptides able to form an immunological complex with a monoclonal antibody, which itself is liable to form a complex with an epitope located in the tau protein region as shown in SEQ ID NO 1 to 4.

The invention also relates to polypeptides (antigens) of about 100 amino acids

which contain the sequence as shown in SEQ ID NO 1 to 4, or

which contain the sequence of the variant peptides defined above.

The invention also relates to the above-mentioned peptides which are liable to generate monoclonal antibodies of the invention.

The invention also relates to a peptide (antigen) which is contained in the brain, in the cerebrospinal fluid, or in the serum of a patient having Alzheimer's disease or any brain disease involving normal human tau protein and which forms an immunological complex with a monoclonal antibody of the invention.

The invention also relates to a peptide (antigen) which is contained in the brain, in the cerebrospinal fluid, or in the serum of a patient having Alzheimer's disease or any brain disease involving PHF or abnormally phosphorylated human tau protein and which forms an immunological complex with a monoclonal antibody of the invention.

A method for preparing the peptides of the invention is characterized in that, preferably starting from the C-terminal amino acid, the successive aminoacyls in the requisite order, or aminoacyls and fragments formed beforehand and already containing several aminoacyl residues in the appropriate order, or alternatively several fragments prepared in this manner beforehand, are coupled successively in pairs, it being understood that care will be taken to protect all the reactive groups carried by these aminoacyls or fragments beforehand except for the amine groups of one and carboxyl groups of the other, or vice versa, which must normally participate in peptide bond formation, in particular after activation of the carboxyl group, according to methods known in peptide synthesis, and so on, proceeding stepwise up to the N-terminal amino acid.

The antigen of the invention, which can be prepared by methods known to those skilled in the art (Lindwall and Cole, 1984) starting from the human cerebral cortex is characterized by its ability to form an immunological complex with the monoclonal antibody of the invention as defined above, advantageously with the monoclonal antibody secreted by the hybridoma AT120 deposited at the ECACC under No. 92100853 on Oct. 8, 1992.

The antigen of the invention is advantageously contained in the brain, in the cerebrospinal fluid or the serum of a patient having Alzheimer's disease, Down syndrome, Pick's disease, subacute sclerosing panencephalitis (SSPE) or other neurological diseases in which the normal tau or abnormally phosphorylated tau protein are implicated; this antigen provokes an immunological reaction with the monoclonal antibody of the invention.

The invention also relates to a process for the detection or the diagnosis in vitro of brain disease involving tau protein, i.e. Alzheimer's disease, which involves:

bringing the monoclonal antibody of the invention into contact with a preparation of NFT containing tau protein or a detergent-extracted brain homogenate containing tau protein isolated from a patient having had Alzheimer's disease or any other disease involving tau protein or abnormally phosphorylated tau protein under conditions suitable for producing an antigen-antibody complex; and,

separating the antigen from said complex and recovering the antigen sought in a purified form.

The preparation of tau can be carried out according to Lindwall and Cole (1984).

Advantageously, the monoclonal antibodies used are in an immobilized state on a suitable support such as a resin. The process for the detection of the antigen can then be carried out as follows:

bringing the supernatant containing proteins and polypeptides obtained as a result of an extraction procedure starting from brain tissues or cerebrospinal fluid known to those skilled in the art (Iqbal et al., 1984; Greenberg and Davies, 1990) into contact with said monoclonal antibody, under such conditions as to allow the formation of an immunological complex;

washing the immobilized antibody-antigen complex then formed;

treating this complex with a solution (e.g. 3 M potassium thiocyanate, 2.5 M magnesium chloride, 0.2 M citrate-citric acid, pH 3.5 or 0.1 M acetic acid) capable of producing the dissociation of the antigen-antibody complex; and;

recovering the antigen in a purified form.

The process of the invention for the detection or diagnosis in vitro of brain disease involving tau protein and abnormally phosphorylated tau protein, as e.g. in Alzheimer's disease, includes:

bringing a sample of a brain homogenate, or of cerebrospinal fluid, or of serum from a patient suspected of suffering from a neurological disorder involving tau protein or PHF, more particularly Alzheimer's disease, into contact under in vitro conditions with the monoclonal antibody of the invention, with said conditions being suitable for producing an antigen-antibody complex; and

detecting the immunological binding of said antibody to said sample of brain homogenate, or of cerebrospinal fluid, or of serum.

The detection of the immunologically bound monoclonal antibody can be achieved by conventional technology. Advantageously, the monoclonal antibody of the invention itself carries a marker or a group for direct or indirect coupling with a marker as exemplified hereafter. Also, a polyclonal antiserum can be used which was raised by injecting the antigen of the invention in an animal, preferably a rabbit, and recovering the antiserum by immunoaffinity purification in which said polyclonal antibody is passed over a column to which said antigen is bound and eluting said polyclonal antibodies by conventional technology, Detection can also be achieved by competition binding of the antigen with a labeled peptide comprising the epitope of the invention.

A particularly advantageous embodiment of the process of the invention for the detection or diagnosis in vitro of brain diseases involving PHF and/or normal tau protein, e.g. Alzheimer's disease, comprises the steps of:

bringing a sample of unconcentrated cerebrospinal fluid sample isolated from a patient suspected of suffering from a neurological disorder involving normal or abnormally phosphorylated tau protein, more particulary Alzheimer's disease, into contact under in vitro conditions with a monoclonal antibody according to the invention, under conditions suitable for producing an antigen-antibody complex; and,

detecting the immunological binding of said antibody to said sample of cerebrospinal fluid by means of a sandwich ELISA, preferably by applying the catalysed reporter diagnosis enhancement (CARD) procedure.

The invention also relates to a kit for the diagnosis in vitro of one of the following diseases: Alzheimer's disease, Down's syndrome, Pick's disease, subacute sclerosing panencephalitis (SSPE) and other neurodegenerative disorders in which normal tau protein or abnormally phosphorylated tau protein are implicated. Such a kit would contain:

at least one microplate for deposition thereon of any monoclonal antibody of the invention;

a preparation containing the sample to be diagnosed in vitro, possibly together with a labeled peptide containing the epitope of the invention and preferably, a peptide lying in the peptide sequence as shown in SEQ ID NO 1 to 4,

a second antibody

* which can be a monoclonal antibody recognizing another epitope of normal or abnormally phosphorylated tau protein, or of any peptide of the invention, with said epitope being different from the one of the invention, or

* which can be a polyclonal antibody directed against normal or abnormally phosphorylated tau, or against a peptide of the invention, with said polyclonal antibody being liable to form an immunological complex with epitopes which are all different from the epitope of the invention, with said polyclonal antibody being preferably purified by immunoaffinity chromatography using immobilized tau protein, or

a marker either for specific tagging or coupling with said second antibody;

appropriate buffer solutions for carrying out the immunological reaction between the monoclonal antibody of the invention and a test sample on the one hand, and the bound second antibody and the marker on the other hand.

The labeled peptide mentioned above can be a peptide which has been labeled by any means known for the man skilled in the art. Moreover, the marker specific for tagging and coupling can be any marker known to the man skilled in the art.

The invention also relates to a kit, as described above, also containing the antigen of the invention, with said antigen of the invention being either a standard (for quantitative determination of the antigen which is sought) or a competitor, with respect to the antigen which is sought, for the kit to be used in a competition dosage process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

Western blotting detection of normal tau or PHF-tau using the monoclonal antibodies Tau-1, (Binder et al., 1985) AT8 (Mercken et al., 1992b) and AT120. Lanes 1, 3 and 5: PHF-tau isolated according to Greenberg and Davies (1990). Lanes 2, 4 and 6: Normal affinity purified human tau according to Mercken et al. (1992a). Lane 7: Molecular weight markers.

Lanes 1 and 2 were developed using AT8, lanes 3 and 4, using AT120 and lanes 5 and 6, using Tau-1 monoclonal antibody.

FIG. 2A and FIG. 2B

Detection of tau protein by immunochemistry

FIG. 2A: section from hippocampus of a patient with Alzheimer's disease. Magnification 212×.

FIG. 2B: section from another hippocampus of a patient with Alzheimer's disease with abundant tangles. Magnification 212×.

FIG. 3

Titration of normal (0) and PHF tau (▪), spiked in a tau-negative CSF pool using the amplified (CARD) AT120 sandwich ELISA. All dilutions were tested in duplicate and the data presented as optical density (OD) units.

FIG. 4

Western blotting of several deletion mutants constructed as indicated in example V, and stained with AT120 as indicated in Example I. Mutants comprise the following amino acids (AA); Lane 1, full length tau 34 (Goedert et al., 1989); Lane 2, amino terminus of tau 34 up to AA₁₅₄; Lane 3, from AA₁₅₅ to the carboxyterminus of tau 34; Lane 4; aminoterminus of tau 34 up to AA₂₄₂; Lane 5, aminoterminus tau 34 up to AA₂₂₁; Lane 6, from AA₂₂₂ to the carboxyterminus of tau 34.

FIG. 5 Epitope recognition sites of the monoclonal antibodies HT7, BT2, AT8 are depicted on the epitope of the invention (SEQ ID NO 1) shown in the one letter amino acid code. Epitopes are boxed. The star “*” designates the fact that the AT8 epitope recognition needs phosphorylation of serine residue 202.

FIG. 6

Complete sequence of the mTHFMPH-tau1 fusion protein (SEQ ID NO 23) with indication of relevant restriction sites.

EXAMPLES Example I

Preparation of the monoclonal antibody AT120 (IgG1, subtype kappa)

1. Preparation of the Antigen for Immunization

PHF-tau was partially purified by a modification of the method of Greenberg and Davies (1990). Postmortem tissue, consisting mostly of gray matter from the frontal and temporal cortex, was obtained from histologically confirmed Alzheimer patients. This Alzheimer gray matter brain sample (5-10 g) was homogenized with 10 volumes of cold buffer H (10 mM Tris/1 mM EGTA/0.8 M NaCl/10% sucrose, pH 7.4) in a Teflon/glass Potter S (Braun, Germany) homogenizer. After centrifugation of the homogenate in a 60 Ti MSE rotor at 27,000×g for 20 min at 4° C., the pellet was removed and the supernatant was adjusted to 1% (wt/vol) N-laurosylsarcosine and 1% (vol/vol) 2-mercaptoethanol and incubated while rotating on a mixer (Swelab, Sweden) for 2.5 hours at 37° C. The supernatant mixture was centrifuged at 108,000×g for 35 min at 20° C. The PHF-tau containing pellet was gently washed with PBS and finally suspended in 1 ml of the same buffer.

The antigen preparation was evaluated by a 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by Western blotting using immunoblotting with polyclonal rabbit antihuman normal tau antiserum (Mercken et al., 1992b).

2. Immunization Protocol and Fusion Procedure

Balb/c mice were primed subcutaneously with 100 μg partially purified PHF-tau in complete Freund's adjuvant and boosted intraperitoneally 3 times thereafter at 3-week intervals with 100 μg of the same antigen in incomplete Freund's adjuvant. On days 3 and 2 before the fusion, mice were boosted with 100 μg PHF-tau in saline.

Mouse spleen cells were fused with SP2/0 myeloma cells, using a modified procedure of Köhler and Milstein (1975), with PEG 4000.

The cells of the fusion experiment were suspended at a density of 4.5×10⁴ spleen cells/well on 96-well plates preseeded with mouse peritoneal macrophage cells as a feeder layer. These wells were screened after 12 days for anti-tau antibody production in a sandwich ELISA either specific for normal tau or for PHF-tau as discussed in section 3. below.

Hybridoma growth was in Dulbecco's modified Eagle's medium (DMEM) supplemented with 20% fetal calf serum, sodium pyruvate (1 mM), L-glutamine (2 mM), penicillin (100 U/ml), streptomycin (100 mg/ml), and nonessential amino acids. All products were purchased from Gibco, (Paisley, U.K.). Cells were incubated in a humidified CO₂-air incubator.

3. Sandwich ELISA for Antibody Screening

The screening ELISA used for the detection of anti-tau monoclonal antibodies was a sandwich ELISA system with affinity-purified polyclonal rabbit anti-human tau antibodies (Mercken et al; 1992a) in the coating phase. To this end, purified human normal tau, prepared as described in Mercken et al. (1992a) was used for the preparation of an immuno-affinity column using cyanogen bromide-activated Sepharose (Pharmacia, LKB Sweden). The affinity-bound anti-tau fraction was eluted from this column with a 0.1 M citric acid buffered solution at pH 2.5. After neutralization, the anti-tau-containing fractions were pooled and coated overnight (1 μg/ml) at 4° C. on high-binding microtiter plates (Nunc, Gibco, Paisley, UK) in coating buffer (10 mM Tris, 10 mM NaCl, 10 mM NaN₃, pH 8.5). After overcoating for 30 min with 125 μl 10%-saturated casein in PBS to reduce non-specific binding, the plates were incubated with 100 μl of an appropriately diluted PHF-tau preparation and incubated for 60 min at 37° C. The plates were washed 3 times with PBS-0.05% Tween 20 (v/v); 100 μl hybridoma supernatant was added and incubation was continued for 1 h at 37° C. After washing, the bound monoclonal antibodies were detected with peroxidase-conjugated rabbit anti-mouse serum (Dakopatts, Glostrup, Denmark). All reagents were diluted in PBS with 10% casein. After final washing, 100 μl 0.42 mM 3,5,3′,5′-tetramethylbenzidine, 0.003% H₂O₂ v/v in 100 mM citric acid, 100 mM disodium hydrogen phosphate, pH 4.3, was added as peroxidase substrate. The reaction was stopped with 50 μl of a 2 M H₂SO₄ solution. Absorbance was read in a Titertek Multiscan (Flow Laboratories, Eflab, Oy, Finland) at 450 nm.

The cross-reactivity of the monoclonal antibodies with normal tau in ELISA was tested in a sandwich ELISA identical to the screening assay, except that affinity-purified normal tau was used as the antigen instead of PHF-tau.

At the first selection of positive hybridoma cultures, most positive cultures were initially composed of mixed clones as seen by visual inspection of the wells (3-4 clones per well). These positive cultures were arbitrarily designated AT1 to AT24 (some of these hybridoma cultures, i.e., AT1 to AT14 were described by Mercken et al., 1992b). After this initial screening round, hybridoma cultures were subcloned by limiting dilution, a technique well-know to those skilled in the art, finally resulting in pure hybridoma clones secreting antibodies with a homogeneous idiotype. These pure hybridoma clones were further tested with respect to their reactivity pattern on normal and PHF-tau in ELISA, Western blotting and immunohistochemistry, and to their capability to diagnose neurological diseases by means of their affinity for tau protein present in an undiluted sample of cerebrospinal fluid. Based on these criteria, the monoclonal antibody AT120 was selected and further characterized as shown in the following examples.

4. Determination of the Antibody Class and Subclass

The antibody class and subclass was determined by Inno-LIA (Innogenetics, Ghent, Belgium). The antibody of the invention, AT 120, appeared to be of the IgG1, kappa subtype.

Example II

Detection of Pathological Tau and Normal Tau in ELISA and by Western Blotting

1. Detection of Normal Tau in ELISA using AT120.

Protein G-purified monoclonal antibody AT120, obtained from serum-free hybridoma AT120 conditioned medium, was coated on ELISA plates and reacted with different dilutions of affinity-purified human normal tau as described in Mercken et al. (1992a), prepared in a solution of PBS and 10% casein.

The purity of normal tau was determined by SDS-PAGE. Tau samples were analyzed on an 420 A/H amino acid analyzer (Applied Biosystems B. V., Maarssen, The Netherlands) according to the manufacturer's instructions and the protein showed the expected amino acid composition. From the amino acid composition and by comparison with a standard peptide the concentration of normal tau was determined.

After incubation of the ELISA plates with different concentrations of tau spiked in tau- and PHF-tau-negative CSF for 1 h at room temperature, the plates were washed and incubated with 0.2 μg/ml biotynilated BT2 and HT7, each recognizing an epitope different from the AT120 epitope and present on normal term. After washing, complexed biotynilated antibodies were detected with horseradish peroxidase conjugated streptavidine (Jackson) and color development as specified in example I. The results are shown in Table I and FIG. 3.

TABLE I Detection of normal tau in ELISA ABSORBANCE CONCENTRATION (expressed as milliabsorbance units) (pg/ml) PHF-tau normal tau 160 1682 1609 80 901 970 40 566 678 20 257 256 10 143 154 0 92 87

2. Detection of Pathological Tau and of Normal Tau in Western Blotting Using AT120.

Purified normal human tau and PHF-tau were applied to 10% SDS-polyacrylamide gels and run under denaturing conditions according to Laemmli (1970). After SDS-PAGE, the transfer to nitrocellulose (Hybond-C, Amersham, Brussels, Belgium) was carried out in 10 mM NaHCO₃, 3 mM Na₂CO₃, pH 9.9 for 120 min at 55 V with cooling. After blotting, the nitrocellulose was equilibrated to phosphate buffered saline (PBS), and protein binding sites were blocked with blot buffer (PBS supplemented with 5% w/v skimmed dried milk and 10% v/v newborn calf serum). Blotted proteins were incubated overnight at 4° C. with AT 120 as primary antibody. After 3 washings with PBS-0.05% Tween 20(vv), horseradish peroxidase-labeled rabbit anti-mouse immunoglobulins (Dakopatts, Glostrup, Denmark) were used at a dilution of {fraction (1/3000)} and were incubated for 90 min at room temperature. All antisera were diluted in blot buffer. The blots were then washed three times in PBS/Tween and developed with substrate solution (PBS,0.05% w/v 3,3′-diaminobenzidine, 0.03% v/v H₂O₂) after which the reaction was stopped in H₂O. Results shown in FIG. 1 indicate that the AT120 antibody recognizes all tau isoforms. By contrast, the Tau-1 antibody (Binder et al., 1985) reacts solely with normal tau, and the AT8 antibody (Mercken et al., 1992b) only with PHF-tau.

AT120, AT8 and Tau-1 mAbs were tested for phosphatase sensitivity of their epitopes in ELISA and in Western Blot on PHF-tau antigen. The reactivity of the AT120 antibody with PHF tau was not sensitive to phosphatase treatment either in ELISA (data not shown) or on Western blots (data not shown). The reactivity of AT8 was almost completely abolished after alkaline phosphatase treatment of the PHF-tau antigen in ELISA. Dephosphorylation of PHF-tau enhanced Tau-1 immunoreactivity, as described previously (Binder et al., 1985).

Example III

Detection of Tau by Immunohistochemistry

Paraffin sections of formalin-fixed brain tissue from neocortex, hippocampus, cerebellum, pons, and spinal cord of several Alzheimer patients and age-matched controls were prepared, as well as sections of peripheral nerve from one control patient.

Cryostat sections from Alzheimer and age-matched control brain were also prepared. Tissues were immunostained either with the peroxidase-antiperoxidase (PAP) technique (Steinberger et al., 1970) or with the avidin-biotin complex (ABC) technique (Hsu et al., 1981) using Dakopatts (Denmark) and Amersham (UK) reagents, respectively.

Briefly, after blocking non-specific interactions with normal swine serum (Dakopatts X90 1) diluted 1:25 in Tris-buffered saline (TBS) containing 1% bovine serum albumin (BSA), sections were incubated overnight with the AT120 primary antibody appropriately diluted in TBS/BSA. Secondary antibody and peroxidase complex were then applied for 30 min each, with intermediate rinsing in TBS. Color was developed with 3,3′-diaminobenzidinetetrahydrochloride (Sigma). Sections were counterstained with Harris' liematoxylin, dehydrated, coverslipped, and viewed under a light microscope.

FIGS. 2A and 2B clearly indicate that AT120 produces abundant staining of NFT, dystrophic neurites in plaques, and dispersed staining of neuropil (neuropil threads).

Example IV

Detection of Tau in Cerebrospinal Fluid Samples

Cerebrospinal Fluid Samples

CSF samples from patients were collected at the Department of Neurology office University Hospital of Antwerp, All samples were obtained by lumbar puncture performed for routine diagnostic purposes. CSF samples were frozen and kept at −75° C. in small aliquots until use.

The patients were divided into 3 different groups: 27 patients diagnosed with probable AD according to Mc Khann et al. (1984), mentally healthy control patients, who underwent lumbar puncture for radiculopathy and patients suffering from other neurological diseases (OND). The OND group included inflammatory, vascular, and other diseases, including patients with neurodegenerative diseases such as adenoleukodystrophy, frontal lobe degeneration, cerebellar atrophy, olivo-ponto-cerebellar atrophy, and amyotrophic lateral scelerosis. The age, sex and diagnosis were noted for each patient.

AT120 Assay

AT120 monoclonal antibodies purified from serum-free conditioned medium by Protein G column chromatography were coated overnight at 4° C. on high-binding microtiter plates (Nunc, Gibco, Paisley, UK) in coating buffer at 3 μg/ml (10 mM Tris, 10 mM NaCl, 10 mM NaN₃, pH 8.5). After overcoating for 30 min with 150 μl 10%-saturated casein in PBS to reduce non-specific binding, the plates were incubated with 25 μl CSF and 75 μl conjugate mixture containing 0.2 μg/ml of biotynilated BT₂ and an equal amount of HT7 in 5% Tween 20, 10% saturated casein in PBS. The plates were left overnight at room temperature and after washing peroxidase conjugated streptavidine (Jackson) ({fraction (1/15000)}) was added for 30 minutes at room temperature.

Following an additional washing, 100 μl 0.42 mM 3.5, 3′,5′-tetramethylbenzidine 0.003% H₂O₂ v/v in 100 mM citric acid, 100 mM disodium hydrogen phosphate, pH 4.3, were added as perocidase substrate. The reaction was stopped with 50 μl of a 2M H₂SO₄ solution. Absorbance was read in a Titertech Multiscan (Flow laboratories, Eflab, Oy, Finland) at 450 nm.

Absorbance values obtained with AT120 from the CSF samples were compared with standard curves generated from known quantities of affinity purified normal human tau and this comparison allowed the result to be expressed as pg tau/ml.

A summary of these results are compiled in Table II, where patients ID, diagnosis, age and tau values expressed in pg/ml CSF are listed. From these results, it is obvious that levels of control patients are substantially lower (mean: 16.4 pg/ml) as compared to the groups of patients suffering from various neurological diseases (OND; mean value: 26.4 pg/ml). For patients with Alzheimer's disease the mean value is clearly elevated above those of control and OND samples (mean Alzheimer patient: 50.8 pg/ml). If a cut-off level of 27 pg/ml is adopted, 8% of the control samples are positive, while for the OND group and the Alzheimer group these values are 27% and 80% respectively.

Table II: Tau levels as determined with the AT120 ELISA assay, grouped according to control patients, Alzheimer patients (AD) and other neurological diseases (OND) and according to age cohort, expressed in pg/ml. Mean and Std (=SD) is expressed as pg/ml per age cohort.

Number Diagnosis Age pg/ml mean Std  3 AD (early onset AD) 35 *56.5 33.3 12.3 260 A.D. 41 *31.2 113 A.D. 44 *42.6 161 A.D. (Possibly Creutzfeld) 57 *33.8  81 A.D. 58 *14.5 126 A.D. 59 *24.8 421 A.D. 59 *29.8 338 A.D. 64 *51.2 61.68 35.4 254 A.D. 66 *80.2 209 A.D. 67 *74.4 383 Primary degenerative 67 *32.5 dementia  38 A.D. 67 *68.7 229 A.D. 73 *70.9 132 A.D. 76 *51.9  88 A.D. 76 *25.3  65 Dementia 77 *80.1  71 A.D. 78 *53.9  28 A.D. (early onset A.D.) 78 *48.7  11 A.D. 85 *14  39 A.D. 86 *150 386 control  5 *17.5 17.3 4.37 108 control 20 *14.3 402 control 26 *14 106 control 27 *14 424 control 28 *14 355 control 28 *20.1 399 control 29 *14 373 control 30 *17.4 381 control 31 *14 372 control 32 *19.2 379 control 32 *18.3 241 control 32 *14 415 control 32 *14 428 control 33 *16.6 118 control 34 *21.5 224 control 36 *15.7  24 control 37 *25.2 369 control 38 *23.9 425 control 39 *14 145 control 40 *31.9  61 control 40 *17.3 377 control 40 *14 366 control 41 *17.7 401 control 41 *20.1 400 control 42 *14 417 control 42 *14 354 control 43 *16.8  34 control 43 *25.8 217 control 43 *14 364 control 44 *14 134 control 45 *16.7 367 control 45 *14 427 control 45 *44 394 control 48 *14 361 control 48 *14 237 control 50 *17.2 396 control 52 *16.4 100 control 54 *23.9 411 control 54 *14 371 control 55 *18.4 423 control 56 *14.9  99 control 56 *27.9 192 control 60 *19.9 24.83 15.17 387 control 61 *14 389 control 65 *19.5 426 control 66 *15.4 141 control 67 *14 368 control 67 *15.4  60 control 77 *43.5 348 control 80 *56.9 419 Hydrocephalus  0 *150 29.35 26.78 413 Adenoleukodystrofy 13 *23.1 376 Paresthesia 14 *21.1 239 Epilepsy, encephalitis 16 *29.8  7 SSPE 17 *48.1 139 Cerebellitis (Mycoplasma p.) 18 *19.7 180 Herpes encephalitis 19 *14.1 206 GBS 20 *15.9 140 TC ? 21 *14.2 228 Ishernic cerebral infarct 22 *150 197 Kawasaki 24 *27.8 133 MS 24 *37.1 212 Alcohol PNP 25 *14  66 MS ? 25 *14 143 Myopathy 25 *18.3  82 MS 26 *20.2 258 Guillian-Barré 26 *14.4 105 MS 26 *18.4 169 Dementia? 27 *37.5 351 Viral meningitis 28 *17.3 213 MS 28 *15.7 253 Encephalitis viral ? 28 *38.1 236 Migraine 29 *17.3 465 Guillian-Barré 29 *47.6  72 MS 29 *14 234 MS 29 *19.9 128 GBS 29 *14 138 PNP 32 *17.6 218 Empty sella 35 *14 135 MS 35 *16.3 346 Neuritis optico 35 *14 117 Trigeminus neurology 36 *14 350 MS 37 *14 384 Guillian-Barré 37 *14 123 CVA 38 *14  56 TIA (transient ischemic 39 *14.9 attack) 172 CVA ? psych. 40 *21.7 189 Hemicranial headache 41 *15.9 119 Amyloidosis 42 *15.3  69 Meningitis 42 *26.5 231 Contuno alcohol 42 *15.5 130 External oftalmoplegia 43 *53.6 357 CVA 44 *16.6 391 MS 44 *14  62 MS ?? 44 21.2 124 Syphilis 45 *20.4  89 PNP 45 *27.1 122 Cauda equina syndroom etiol. 46 *14 249 MS 47 *14 112 MS ? 48 *14.9 363 Encephalitis 48 *35.9 125 MS 48 *24.9 205 GBS 49 388 MS 50 *14 418 Tetanos 50 *14 207 GBS ? 50 *70.3 114 Cerebellar atrofy 51 *51.5 121 Syphilis 51 *28.1  35 MS + PNP (diabetic) 51 *17.3 215 OLM 52 *14 101 Brain infarct 53 *52.8 255 PNP + (MS ?), diabetic 53 *18.4 173 Lyme disease 54 *17.5 360 (Borrelia) (MS-like) 54 *34.7 374 ALS 54 *65.3 179 Lyme disease 54 *16.4  50 Epilipsy-alcoholism 55 *21.5 184 Epilepsia 55 *16.7 210 MS 56 *16.2  58 CVA 57 *25.3 137 Pick ? 57 *77.4 . 131 Meningial bleeding 57 *66.7 398 Meningoencephalis 58 *117.8 349 Meningoencephalis 58 *35.6 244 Facialis parese 58 *18.5 219 Pseudobullair syndrome 58 *39.6  64 MS 58 *40.7  36 TIA 59 *14 240 Guillian-Barré  68? *14 25.06 15.69  70 N. ulnaris/Parkinson (?) 60 *23.8 166 tbc 60 *14  85 Aneurism 60 *18.3 204 Bipyramidal idiopathy 60 *16.8 167 Cerebellar atrophy 61 14 157 Bulbar paralysis 62 *17.4  30 Steele Richardson 62 *19.2 153 Lymfoma CSZ 62 *22.2 414 Subacute polyneuropathy 62 *14  37 OPCA 63 *26.7 109 Pick; ALS 63 *40.5 277 COLD 64 *14 195 E, dialysis 64 *14 148 MS 65 *15.4 375 Polyneuropathy, Charot- 65 *15.5 Marie-Tooth 182 ALS 65 *14 230 Parkinson 66 *21.1 409 Multiple vascular (pons.) 66 170 Temp. E 66 *24.2 186 ALS 66 *21.2  59 Menigeal aneurysma 67 *28.4 233 Korsakow-like post trauma 67 *29.6 120 ALS 67 *25.7 550 PNP, CVA, diabetes 67 *64.2 110 Diabetes 67 *14 259 Polyvascular syndrome + 68 demyelinisation 248 (?) 68 *14 235 CVA 68 *77.9 362 Guillain-Barré 68 *14 208 PNP-zona 68 *28.8 115 Subacute combined 68 *14 degeneration  98 TIA 68 *34.9 193 GBS 68 *44.1 222 Guillain-Barré 69 *14.1 102 PNP 70 *14 242 Bipyramidal syndrome PNP 72 *20. 8 251 Trauma cerebri commoti 77 *14 422 Infarct 78 *20.7  42 Multi-infarct dementia 78 *38.9  93 Diabetes, PNP, radiculopathy 85 *61.9  53 Mixed dementia, Parkinson 85 *59.3 Abbreviations: SSPE: Subacute sclerosing panencephalitis, GBS: Guillain-Barr{acute over (e )}syndrome., TC: Meningeal tuberculosis, MS: Multiple sclerosis, PNP: Polyneuropathy, CVA: cerebrovascular amyloidosis, ALS: Amyotrophic lateral sclerosis, TIA: Transient ischemic attack, OPCA: Olivo-ponto cerebellar atrophy, COLD: Chronic obstructive lung disease.

Example V

Definition of the AT120 Epitope

Since AT120 reacts equally well with all isoforms of tau (Goedert et al., 1989), the smallest combinant tau form was used for deletion mapping. To this, two sites were used for deletion construction, the SacII site at position 155 of the human tau 34 sequence and the SmaI site at position 220 (Goedert et al., 1989). A mTNF-fusion vector pmTNF(MPH) (Innogenetics, Ghent, Belgium), in which the smallest tau open reading frame was fused to amino acids of mouse tumor necrosis factor, was cut with Apal-SacII, blunted with T₄ DNA polymerase and ligated. After cutting the ligated material with Sac II and Apa I to reduce non-mutant background, the mixture was transformed into MC1061 pc 1587 (Casadaban & Cohen, (1980)). Each selected clone was further characterized by restriction digestion and by its reactivity with anti-tau antibodies.

The same mouse TNF fusion tau vector was used to insert a frame shift mutation in the XmaI restriction site. The vector was cut with SmaI, blunted with T₄ DNA polymerase and the ligated mixture was retreated with SmaI before transformation in order to reduce non-mutant background. The reactivity pattern of each of the mutants was checked with AT120 monoclonal antibodies by means of Western Blotting. This allowed to localize the epitope of AT120 in a first approximation to the region of 65 amino acids spanning amino acid 155-221 which is represented in SEQ ID NO 1 (FIG. 4). However, since in this region also two other antibodies, BT2 (Mercken et al, 1992a) and HT7 (Mercken, Ph.d. Thesis) show reactivity it was mandatory to prove that no competition binding was observed between the latter monoclonal antibodies and AT120.

Therefore, a competition ELISA with each of these antibodies was performed. To this, affinity purified rabbit anti-human tau polyclonal antibodies were coated overnight at 4° C. in coating buffer (10 mM Tris pH 8.6, 10 mM NaCl, 10 mM NaN₃), and after blocking with 0.1% caseine in PBS, 100 μl well of pure PHF-tau was added for 1 h at 37° C. After washing, 50 μl of either AT8, BT2 or AT120 unlabeled monoclonal antibody was added at a concentration of 10 μg/ml and incubation was continued for 30 min at 37° C. Next, 50 μl of biotinylated monoclonal antibody was added. Each of these biotinylated antibodies was used in a preset concentration, which in a tau Sandwich ELISA (as described in Example II) gave 50% of the maximal OD value. After a subsequent incubation of 1 h at 37° C., the plates were further treated as described in Example II.

TABLE III Competition ELISA using monoclonal antibodies AT8, AT120 and BT2. Unlabeled competitor Absorbance BIOTINYLATED AT8 AT120 BT2 AT8  0.001 0.372 N.D. AT120 0.476 0.001 N.D. BT2  N.D. 0.543 0.054 N.D. refers to not determined absorbances

The results, shown in Table III clearly indicate that the epitope recognized by the monoclonal antibody AT120 is different from the epitopes recognized by the monoclonal antibodies BT2 and AT8. Consequently, solid phase immobilized synthetic nonapeptides, the sequence of which was derived from the epitope of the invention as depicted in SEQ ID NO 1, were incubated with each of these monoclonal antibodies. The complexes were visualised as in Example I, section 3. On the basis of their respective reactivity patterns it was confirmed that the epitope recognized by AT120 is different from that of each of the other monoclonal antibodies (Table IV and FIG. 5)

TABLE IV Reactivity of monoclonal antibodies BT2, HT7 and AT120 with solid phase bound nonapeptides. The nonapeptides are designated in the one-letter amino acid code. Detecting Monoclonal antibody Absorbance Nonapeptides HT7 BT2 AT120 GAAPPGQKG 3.00  0.168 0.089 (SEQ ID NO 5) GDRSGYSSP 0.493 3.00  0.553 (SEQ ID NO 6)

In addition to these experiments, the AT120 epitope was also confirmed by peptide mapping. Hereto, a total of 20 μg of mTNF-MPHtau1 (see FIG. 6) was lyophilized and redissolved in 56 μl of 100 mM Tris HCl containing 10% acetonitrile. To this was added 14 μl of endoprotease Asp N (0.04 μg/ml) and the mixture was incubated for 8 hours at 37° C. Following cleavage, the mixture was divided equally over 5 sample wells and subjected to SDS-polyacrylamide gel electrophoresis. Following electrophoresis, the peptides in the gel were blotted onto a PVDF membrane. A strip of the PVDF membrane corresponding to one lane on the gel was removed. Free binding sites on the membrane were blocked by incubation with 0.5% casein in PBS, and the strip was incubated with the monoclonal antibody AT120 to determine if protein fragments were present which were capable of being recognized. The presence of bound antibody was detected using an alkaline phosphatase-labeled rabbit anti-mouse conjugate followed by incubation with 5-bromo-4-chloro-3-indolyl phosphate and nitro blue tetrazolium. The remainder of the PVDF membrane was stained with Amido Black, which revealed the presence of 5 bands, all with a molecular size smaller than that of the original protein. One of these bands was visible on the portion of the blot which was incubated with AT120. The band which was specifically recognized by AT120 corresponded to the largest of the Amido Black-stained bands with an apparent molecular size of approximately 6 kDa. This band was excised from the Amido Black-stained blot and subjected to amino terminal sequence analysis (Edman degradation). The analysis revealed that the band recognized by AT120 began with Asp193 in the amino acid sequence of tau, close to the C-terminus of the tau sequence contained within the mTNF-MPHtau 1 recombinant protein.

It thus appeared probable, that additional amino acid sequences located downstream with respect to Arg221 might be required for binding of the monoclonal antibody AT120. In order to test this hypothesis in an attempt to further delineate the boundaries of the epitope, peptide (tau5B) was synthesized:

                         208     210                 215 (SEQ ID NO 7) tau5B       Bio-Gly Gly  Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr         220                 225                 230 231 Pro Pro Thr Arg Glu Pro Lys Lys Val Arg Val Val Arg Thr

Since it cannot be excluded that the second glycine residue of the spacer sequence is functionally equivalent to Gly207, the position of the epitope bound by AT120 must lie between Gly207 and Thr231.

In order to localize the epitope within the sequence of peptide tauSB even more precisely, overlapping 12-mers spanning the tau5B sequence were synthesized in quadruplicate as defined spots on Whatman 1MM paper. The paper was first derivatized with two residues of β-alanine to provide the paper with a handle on which peptide synthesis could take place. The first of these β-alanine residues was coupled as a symmetric anhydride in the presence of 1 equivalent of dimethylaminopyridine. The second β-alanine residue was coupled following in situ activation using 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate in the presence of 1-hydroxybenzotriazole. The coupling of all additional amino acids was performed using the same chemistry (Knorr et al., 1989). The peptides synthesized and their recognition by AT120 were as follows:

PEPTIDE SEQUENCE REACTION WITH AT120 GGSRSRTPSLPT  (SEQ ID NO 8) −  GSRSRTPSLPTP  (SEQ ID NO 9) −   SRSRTPSLPTPP  (SEQ ID NO 10) −    RSRTPSLPTPPT  (SEQ ID NO 11) −     SRTPSLPTPPTR  (SEQ ID NO 12) −      RTPSLPTPPTRE  (SEQ ID NO 13) −       TPSLPTPPTREP  (SEQ ID NO 14) −        PSLPTPPTREPK  (SEQ ID NO 15) +++         SLPTPPTREPKK  (SEQ ID NO 16) +++          LPTPPTREPKKV  (SEQ ID NO 17) +++           PTPPTREPKKVA  (SEQ ID NO 18) +++            TPPTREPKKVAV  (SEQ ID NO 19) +++             PPTREPKKVAVV  (SEQ ID NO 20) +++              PTREPKKVAVVR  (SEQ ID NO 21) −               TREPKKVAVVRT  (SEQ ID NO 22) −

From this experiment, it is evident that the epitope recognized by AT120 is a linear sequence comprised of amino acids Pro218 to Lys224 as specified in SEQ ID NO 4.

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24 67 Amino Acid Unknown Unknown unknown 1 Arg Gly Ala Ala Pro Pro Gly Gln Lys Gly Gln Ala 1 5 10 Asn Ala Thr Arg Ile Pro Ala Lys Thr Pro Pro Ala 15 20 Pro Lys Thr Pro Pro Ser Ser Gly Glu Pro Pro Lys 25 30 35 Ser Gly Asp Arg Ser Gly Tyr Ser Ser Pro Gly Ser 40 45 Pro Gly Thr Pro Gly Ser Arg Ser Arg Thr Pro Ser 50 55 60 Leu Pro Thr Pro Pro Thr Arg 65 33 Amino Acid Unknown Unknown unknown 2 Ser Pro Gly Ser Pro Gly Thr Pro Gly Ser Arg Ser 1 5 10 Arg Thr Pro Ser Leu Pro Thr Pro Pro Thr Arg Glu 15 20 Pro Lys Lys Val Ala Val Val Arg Thr 25 30 13 Amino Acid Unknown Unknown unknown 3 Gly Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr Pro Pro 1 5 10 7 Amino Acid Unknown Unknown unknown 4 Pro Pro Thr Arg Glu Pro Lys 1 5 9 Amino Acid Unknown Unknown unknown 5 Gly Ala Ala Pro Pro Gly Gln Lys Gly 1 5 9 Amino Acid Unknown Unknown unknown 6 Gly Asp Arg Ser Gly Tyr Ser Ser Pro 1 5 26 Amino Acid Unknown Unknown unknown 7 Gly Gly Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr 1 5 10 Pro Pro Thr Arg Glu Pro Lys Lys Val Arg Val Val 15 20 Arg Thr 25 12 Amino Acid Unknown Unknown unknown 8 Gly Gly Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr 1 5 10 12 Amino Acid Unknown Unknown unknown 9 Gly Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr Pro 1 5 10 12 Amino Acid Unknown Unknown unknown 10 Ser Arg Ser Arg Thr Pro Ser Leu Pro Thr Pro Pro 1 5 10 12 Amino Acid Unknown Unknown unknown 11 Arg Ser Arg Thr Pro Ser Leu Pro Thr Pro Pro Thr 1 5 10 12 Amino Acid Unknown Unknown unknown 12 Ser Arg Thr Pro Ser Leu Pro Thr Pro Pro Thr Arg 1 5 10 12 Amino Acid Unknown Unknown unknown 13 Arg Thr Pro Ser Leu Pro Thr Pro Pro Thr Arg Glu 1 5 10 12 Amino Acid Unknown Unknown unknown 14 Thr Pro Ser Leu Pro Thr Pro Pro Thr Arg Glu Pro 1 5 10 12 Amino Acid Unknown Unknown unknown 15 Pro Ser Leu Pro Thr Pro Pro Thr Arg Glu Pro Lys 1 5 10 12 Amino Acid Unknown Unknown unknown 16 Ser Leu Pro Thr Pro Pro Thr Arg Glu Pro Lys Lys 1 5 10 12 Amino Acid Unknown Unknown unknown 17 Leu Pro Thr Pro Pro Thr Arg Glu Pro Lys Lys Val 1 5 10 12 Amino Acid Unknown Unknown unknown 18 Pro Thr Pro Pro Thr Arg Glu Pro Lys Lys Val Ala 1 5 10 12 Amino Acid Unknown Unknown unknown 19 Thr Pro Pro Thr Arg Glu Pro Lys Lys Val Ala Val 1 5 10 12 Amino Acid Unknown Unknown unknown 20 Pro Pro Thr Arg Glu Pro Lys Lys Val Ala Val Val 1 5 10 12 Amino Acid Unknown Unknown unknown 21 Pro Thr Arg Glu Pro Lys Lys Val Ala Val Val Arg 1 5 10 12 Amino Acid Unknown Unknown unknown 22 Thr Arg Glu Pro Lys Lys Val Ala Val Val Arg Thr 1 5 10 391 Amino Acid Unknown Unknown unknown 23 Met Val Arg Ser Ser Ser Gln Asn Ser Ser Asp Lys 1 5 10 Pro Val Ala His Val Val Ala Asn His Gln Val Glu 15 20 Glu Gln Gly Ile His His His His His His Val Asp 25 30 35 Pro Gly Pro Met Ala Glu Pro Arg Gln Glu Phe Glu 40 45 Val Met Glu Asp His Ala Gly Thr Tyr Gly Leu Gly 50 55 60 Asp Arg Lys Asp Gln Gly Gly Tyr Thr Met His Gln 65 70 Asp Gln Glu Gly Asp Thr Asp Ala Gly Leu Lys Ala 75 80 Glu Glu Ala Gly Ile Gly Asp Thr Pro Ser Leu Glu 85 90 95 Asp Glu Ala Ala Gly His Val Thr Gln Ala Arg Met 100 105 Val Ser Lys Ser Lys Asp Gly Thr Gly Ser Asp Asp 110 115 120 Lys Lys Ala Lys Gly Ala Asp Gly Lys Thr Lys Ile 125 130 Ala Thr Pro Arg Gly Ala Ala Pro Pro Gly Gln Lys 135 140 Gly Gln Ala Asn Ala Thr Arg Ile Pro Ala Lys Thr 145 150 155 Pro Pro Ala Pro Lys Thr Pro Pro Ser Ser Gly Glu 160 165 Pro Pro Lys Ser Gly Asp Arg Ser Gly Tyr Ser Ser 170 175 180 Pro Gly Ser Pro Gly Thr Pro Gly Ser Arg Ser Arg 185 190 Thr Pro Ser Leu Pro Thr Pro Pro Thr Arg Glu Pro 195 200 Lys Lys Val Ala Val Val Arg Thr Pro Pro Lys Ser 205 210 215 Pro Ser Ser Ala Lys Ser Arg Leu Gln Thr Ala Pro 220 225 Val Pro Met Pro Asp Leu Lys Asn Val Lys Ser Lys 230 235 240 Ile Gly Ser Thr Glu Asn Leu Lys His Gln Pro Gly 245 250 Gly Gly Lys Val Gln Ile Val Tyr Lys Pro Val Asp 255 260 Leu Ser Lys Val Thr Ser Lys Cys Gly Ser Leu Gly 265 270 275 Asn Ile His His Lys Pro Gly Gly Gly Gln Val Glu 280 285 Val Lys Ser Glu Lys Leu Asp Phe Lys Asp Arg Val 290 295 300 Gln Ser Lys Ile Gly Ser Leu Asp Asn Ile Thr His 305 310 Val Pro Gly Gly Gly Asn Lys Lys Ile Glu Thr His 315 320 Lys Leu Thr Phe Arg Glu Asn Ala Lys Ala Lys Thr 325 330 335 Asp His Gly Ala Glu Ile Val Tyr Lys Ser Pro Val 340 345 Val Ser Gly Asp Thr Ser Pro Arg His Leu Ser Asn 350 355 360 Val Ser Ser Thr Gly Ser Ile Asp Met Val Asp Ser 365 370 Pro Gln Leu Ala Thr Leu Ala Asp Glu Val Ser Ala 375 380 Ser Leu Ala Lys Gln Gly Leu 385 390 1173 Nucleic Acid Double Stranded Unknown unknown 24 ATGGTAAGAT CAAGTAGTCA AAATTCGAGT GACAAGCCTG 40 TAGCCCACGT CGTAGCAAAC CACCAAGTGG AGGAGCAGGG 80 AATTCACCAT CACCATCACC ACGTGGATCC CGGGCCCATG 120 GCTGAGCCCC GCCAGGAGTT CGAAGTGATG GAAGATCACG 160 CTGGGACGTA CGGGTTGGGG GACAGGAAAG ATCAGGGGGG 200 CTACACCATG CACCAAGACC AAGAGGGTGA CACGGACGCT 240 GGCCTGAAAG CTGAAGAAGC AGGCATTGGA GACACCCCCA 280 CCCTGGAAGA CGAAGCTGCT GGTCACGTGA CCCAAGCTCG 320 CATGGTCAGT AAAAGCAAAG ACGGGACTGG AAGCGATGAC 360 AAAAAAGCCA AGGGGGCTGA TGGTAAAACG AAGATCGCCA 400 CACCGCGGGG AGCAGCCCCT CCAGGCCAGA AGGGCCAGGC 440 CAACGCCACC AGGATTCCAG CAAAAACCCC GCCCGCTCCA 480 AAGGCACCAC CCAGCTCTGG TGAACCTCCA AAATCAGGGG 520 ATCGCAGCGG CTACAGCAGC CCCGGCTCCC CAGGCACTCC 560 CGGCAGCCGC TCCCGCACCC CGTCCCTTCC AACCCCACCC 600 ACCCGGGAGC CCAAGAAGGT GGCAGTGGTC CGTACTCCAC 640 CCAAGTCGCC GTCTTCCGCC AAGAGCCGCC TGCAGACAGC 680 CCCCGTGCCC ATGCCAGACC TGAAGAATGT CAAGTCCAAG 720 ATCGGCTCCA CTGAGAACCT GAAGCACCAG CCGGGAGGCG 760 GGAAGGTGCA AATAGTCTAC AAACCAGTTG ACCTGAGCAA 800 GGTGACCTCC AAGTGTGGCT CATTAGGCAA CATCCATCAT 840 AAACCAGGAG GTGGCCAGGT GGAAGTAAAA TCTGAGAAGC 880 TTGACTTCAA GGACAGAGTC CAGTCGAAGA TTGGGTCCCT 920 GGACAATATC ACCCACGTCC CTGGCGGAGG AAATAAAAAG 960 ATTGAAACCC ACAAGCTGAC CTTCCGCGAG AACGCCAAAG 1000 CCAAGACAGA CCACGGGGCG GAGATCGTGT ACAAGTCGCC 1040 AGTGGTGTCT GGGGACACGT CTCCACGGCA TCTCAGCAAT 1080 GTCTCCTCCA CCGGCAGCAT CGACATGGTA GACTCGCCCC 1120 AGCTCGCCAC GCTAGCTGAC GAGGTGTCTG CCTCCCTGGC 1160 CAAGCAGGGT TTG 1173 

What is claimed is:
 1. An isolated human tau peptide epitope which specifically binds monoclonal antibody AT120 consisting of the amino acid sequence selected from the group consisting of SEQ ID Nos. 2, 3, 4, 15, 16, 17, 18, 19 and
 20. 2. The peptide of claim 1 further comprising a label. 